Aspirators are used for inflating emergency devices such as aircraft emergency slides and life rafts as well as simple floatation devices. These devices are quickly inflated with aspirators utilizing the Venturi effect with a pressurized gas, usually air, to quickly inflate a device.
An aspirator is a type of ejector-jet pump that produces a vacuum by means of the Venturi effect. The fluid, a compressed gas, flows through a tube which then narrows. When the tube narrows, the fluid's speed increases, and because of the Venturi effect, its pressure decreases. The velocity energy creates a low pressure zone that can draw in and entrain a suction fluid, which may be air at atmospheric pressure. After passing through the throat of the aspirator, the mixed fluid expands and the velocity is reduced, which results in recompressing the mixed compressed gas and atmospheric air into pressure energy. The compression ratio of the aspirator is the ratio of the aspirator's outlet pressure P2 to the inlet pressure of the suction fluid P1, that is, P2/P1, while the entrainment ratio of the aspirator is the amount of the motive fluid Ws required to entrain and compress a given amount Wv of suction fluid, that is, Ws/Wv. The compression ratio and entrainment ratio are key parameters in aspirator design. FIG. 1 depicts the general principles of an aspirator 10, both of this invention and of the prior art. High pressure gas, maintained within a pressurized container, is injected into aspirator 10 through high pressure inlet fitting 12. The high pressure gas entering into aspirator 10 passes through the converging portion and diverging portion of aspirator 10, creating a pressure drop behind the high pressure gas injectors. The decreased gas pressure draws gas into the atmospheric air aspiration port 14. The atmospheric air mixes with the compressed gas within the body of aspirator 10, the mixed gas and air being expelled from exhaust port 16 of aspirator 10. Exhaust port 16 is positioned within the inflatable device.
The construction of current aspirators is complicated, making the aspirators expensive. The construction also results in physical limitations that affect airflow through the aspirator. FIGS. 2-4 depict a prior art aspirator and its construction. As can be seen in FIG. 2, prior art aspirator 210 comprises an aspirator body 220. High pressure inlet fitting 212, which may be stainless steel, is threaded into aspirator body 220 adjacent to aspiration port 214 and opposite exhaust port 216. Compressed gas, typically air or CO2 injected into aspirator body 220 through high pressure inlet fitting 212 draws atmospheric air into aspirator body 220 through aspiration port 214 where it is mixed before being expelled through exhaust port 216. A plastic black coating is also shown over the surface of aspirator body 220 at and adjacent to exhaust port 216, but does not enter into operation of the aspirator.
FIG. 3 is a view of prior art aspirator along its longitudinal axis from atmospheric air aspiration port 214. A high pressure gas distributor 222 is positioned along the longitudinal axis of aspirator 210. High pressure gas distributor 222 comprises a high pressure inlet port 224 extending through a wall of body 220 to provide fluid communication to the interior of aspirator body 220. High pressure inlet port 224 is attached to high pressure gas distributor conduit 226 having a nozzle array 228 which distributes compressed gas by discharging it toward the converging/diverging nozzle portion in aspirator body 220 and parallel to the longitudinal axis of aspirator body 220. It should be noted that gas from high pressure inlet fitting 212 entering aspirator body 220 perpendicular to longitudinal axis turns 90° within high pressure gas distributor 222 so that it may exit the nozzle array 228 parallel to the longitudinal axis of body 220.
The nozzle array 228 and high pressure inlet port 224 may be assembled to high pressure gas distributor conduit 226 by brazing or welding, and high pressure gas distributor 222 may be assembled to aspirator body 220 at or through the wall by brazing or welding. High pressure gas distributor conduit 226 serves as a manifold for high pressure gas flowing to and discharged from the nozzle array 228. Thus, the fabrication of the high pressure gas distributor conduit 226 and the attachment of the high pressure gas distributor conduit 226 to aspirator body 220 require a number of steps that includes not only intricate machining, but also high temperature processing, all of which contributes to the high cost of the aspirator. FIG. 4 is another view of the aspirator viewed parallel to the longitudinal axis of aspirator body 220, clearly showing high pressure gas distributor 222 with its centerline coincident with the longitudinal axis of aspirator body 220, and nozzle array 228 extending parallel to the longitudinal axis of aspirator body 220. The position of the high pressure gas distributor conduit 226 along the centerline of aspirator body 220 interferes with flow of atmospheric air drawn into aspirator 210 from aspiration port 214.
What is needed is an aspirator that is simpler to fabricate. Simplicity in manufacturing ideally should lead to a concomitant reduction in cost. The aspirator should also desirably provide laminar flow of both high pressure gas and atmospheric air, providing for a more efficient aspirator.